A pressure sore is any lesion caused by excessive, unrelieved pressure on an area of the body. When pressures above normal homeostatic pressure are applied to a body region and its associated blood vessels, the blood vessels can partially or fully collapse, thereby disrupting normal circulation. As a result, the affected area becomes devoid of blood supply, which prohibits oxygen and nutrients from being delivered to the surrounding tissue. Pressure sores often occur over bony prorninences, and can range in severity from partial thickness skin loss to full thickness skin loss with tissue necrosis and damage to underlying muscle and bone.
Pressure sores are a common and costly problem in bed and chair-bound individuals, as well as in patients having an impaired ability to reposition themselves, such as those on ventilators or under anesthesia. In such individuals, various areas of the body may be permanently or almost permanently in contact with the support surface of the bed or chair, resulting in excessive pressure, lack of air circulation, and often increased shear between the contacted body area and the support surface.
Various systems have been proposed to reduce or prevent pressure sores. Among the most common prevention systems are mattresses, cushions, or pads that include some type of raised members extending from a flat base as shown, for example, in U.S. Pat. No. 5,153,956 issued to Nold. The raised members are spaced apart and designed to contact the body at numerous points in an attempt to lower the pressure between the affected body area and the support surface and equalize the pressure over the entire surface of the body. In order to be effective in this capacity, the raised members are designed to be of a height sufficient to maintain the body away from the base. However, upon the application of pressure by contact with the body, the raised members tend to bend and collapse into contact with the base, such that the body is resting against a substantially flat surface with broad points of contact. This action negates any lowering of pressure of the affected area, while also decreasing aeration and increasing the potential for shear between the body member and the pad.